#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
#include<math.h>
int main()
{
    int a = 0;
    int b = 0;
    int c = 0;
    scanf("%d%d%d", &a, &b, &c);

    double s = 0.0;
    double area = 0.0;

    s = (a + b + c) / 2.0;
    area = sqrt(s * (s - a) * (s - b) * (s - c));
    printf("%.2lf", area);
    return 0;
}